U.S. Pat. No. 4,218,240 to Gingerich, et al. relates to a process wherein cobalt is recovered by treating aqueous solutions containing ammonia and cobalt irons with sufficient amount of an acid in the presence of a catalyst to convert the cobalt irons to a cobalt hexammine ion which is precipitated and separated from the resulting solution. The precipitate is dissolved in an aqueous solution to form a relatively pure solution which is treated with a metallic hydroxide to form a cobalt containing precipitate which is reduced to form fine particles of cobalt.
According to the above basic process, some silver may be removed during the normal purification steps during filtration of the aqueous cobaltic hexammine solution. Transition metals are removed by filtration at a pH of about 7.0 but silver chloride or a complex of silver is soluble at these conditions and is not removed from the cobalt containing filtrate. Typical scrap materials may contain relatively large amounts of silver due to the use of silver in brazing alloys so that the above problem is detrimental to the production of high purity cobalt powder.